Two-dimensional differential interference quantitative phase microscopic imaging system based on active liquid crystal polarization grating

Abstract

The invention discloses a two-dimensional differential interference quantitative phase microscopic imaging system based on an active liquid crystal polarization grating. According to the invention, two-dimensional quantitative DIC imaging can be realized through a special light path design based on the strong light field regulation and control capability of the active liquid crystal grating, and the problem that a traditional DIC system can only carry out nonlinear imaging in one direction is solved; according to the invention, the liquid crystal grating with a small volume is adopted to replace an optical refraction element with a large volume in a traditional DIC system, so that a more compact optical path design is realized, the current requirements on miniaturized and lightweight optical devices are met, the optical grating can be easily integrated into other microscopic imaging equipment, multi-modal imaging is realized, and the application range of the optical grating is greatly expanded; the active liquid crystal grating is adopted, the state of liquid crystal molecules is controlled through an external circuit, rapid switching of an imaging mode between bright field imaging and two-dimensional quantitative DIC imaging can be achieved, and the requirements for sample observation under different conditions are met.

Description

Technical Field

[0001] The invention relates to the technical field of microscopic imaging, and in particular to a two-dimensional differential interference quantitative phase microscopic imaging system based on an active liquid crystal polarization grating. Background Art

[0002] The information of the light field can be characterized by parameters such as amplitude, polarization, phase, and frequency. When the light field interacts with matter, the information it carries can reflect the physical and chemical properties of the object. For example, spectral information can reflect the elemental composition of the substance, amplitude information can be used to measure the transmittance of the object, and phase information contains the three-dimensional refractive index distribution of the object. However, because the human eye or photoelectric sensors are insensitive to the phase information of the light field, traditional optical imaging systems often ignore the important phase information, and direct measurement of phase information has always been a difficult problem. Over the past half century, with the development of laser technology, phase measurement technology represented by the interference principle has played a prominent role in metrology. Today, phase imaging technology is widely used in ultra-precision measurement, adaptive optics, biomedical imaging and other fields.

[0003] In the field of label-free biological living cell imaging, phase imaging technology can be used to identify cell size, morphology and characteristic structure. Under traditional bright field microscopes, since most organelles of biological cells have very weak absorption of light, the amplitude of light waves will not change significantly, making it difficult to observe the internal structure of cells. Traditional methods often use fluorescent staining technology to enhance imaging contrast to facilitate observation. However, the fluorescent dyes and fluorescent proteins used in this method will have a great impact on the activity of cells, severely limiting the observation and research of living cells. In 1942, Zernike invented the Zernike phase contrast microscope, which converts the phase information of the object into intensity information through a special phase filter, so that tissue cells can be observed without staining. Subsequently, Nomarski invented the differential interference contrast (DIC) microscope in 1952 based on the principles of polarization beam splitting and shear interference, which can present a relief-like pseudo-three-dimensional pattern related to the optical density of the cell on the image plane.

[0004] Although the above methods have made great progress in the field of phase imaging, there are still three problems. First, the intensity measured by this type of method has a nonlinear relationship with the phase of the sample, which makes it impossible to quantitatively recover the phase information. This is a more serious problem for some research fields that require accurate phase data. Second, the volume is large. Since large refractive prisms are usually required in the optical path, a compact optical system cannot be realized, which greatly limits its scope of application, especially for biological samples that need to be observed for a long time in special incubators. The excessive volume will cause many additional problems. Third, multimodal conversion is difficult. In some studies, it is necessary to observe the intensity and phase information of the sample at the same time. However, traditional phase imaging requires precise calibration of the optical components of the system to achieve the predetermined function, and it is impossible to quickly switch functions between bright field microscopy systems and phase microscopy systems, which causes great inconvenience to the research.

[0005] In recent years, the emergence of new optical devices has provided a new solution for quantitative phase imaging. Active Liquid Crystal Polarization Grating (active LCPG) has excellent light field control performance and is thin and light. It can be used to replace the Wollaston prism in differential interference microscope to achieve a more compact imaging system. At the same time, active liquid crystal grating can achieve rapid conversion of liquid crystal state by controlling voltage, thereby achieving rapid conversion of multiple imaging modes. At the same time, after a certain optical path design, quantitative phase imaging can be achieved, which well solves the above three problems.

[0006] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art known to a person skilled in the art. Summary of the invention

[0007] The purpose of the present invention is to provide a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating in view of the deficiencies of the prior art.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] According to a first aspect of the present specification, a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating is provided, the system comprising:

[0010] Illumination system components, including lasers, beam expanders, collimators, and linear polarizers, are used to provide a suitable illumination source for the sample;

[0011] Active liquid crystal polarization grating component, the periodic arrangement of liquid crystal molecules in the liquid crystal polarization grating can deflect light of different polarization states in different directions, forming +1 and -1 order diffraction light, thereby realizing DIC imaging of the sample in a certain direction. The present invention uses 4 active LCPGs, which are arranged behind the sample, wherein 2 LCPGs whose liquid crystal molecules periodically change in the x direction (hereinafter referred to as xLCPG) and 2 LCPGs whose liquid crystal molecules periodically change in the y direction (hereinafter referred to as yLCPG) are arranged alternately, wherein 1 xLCPG and 1 yLCPG form a fixed LCPG group, and the spacing between the two LCPG groups can be adjusted by a precision mechanism, thereby realizing differential interference contrast imaging with adjustable resolution;

[0012] A microscopic system, arranged behind the active liquid crystal polarization grating assembly, for realizing conventional microscopic imaging;

[0013] The polarization camera is placed after the microscope system to obtain the image formed by the microscope objective and realize differential interference quantitative phase microscopy imaging. The polarization camera is specially designed, and a specially designed polarization filter array is placed in front of the traditional detector, which can capture 4 images with different polarization states at the same time. After the 4 images are processed by calculation, accurate quantitative phase imaging can be achieved;

[0014] A mechanical control component is arranged between the two LCPG groups and is used to adjust the distance between the two LCPG groups, thereby achieving adjustment of the resolution;

[0015] The electrical control component is connected to the active LCPG and is used to control the arrangement state of the LCPG liquid crystal molecules, thereby achieving multi-directional DIC imaging and rapid switching between different imaging modes. Figure 1 , Attachment Figure 2 As shown, when the active liquid crystal polarization grating is not powered on, the liquid crystal molecules of the liquid crystal polarization grating are arranged and distributed according to the designed period Λ, producing the effect of a grating, and producing deflection effects in different directions for circularly polarized light of different polarization states, thereby realizing the lateral shearing of light; while when the active liquid crystal polarization grating is powered on, the liquid crystal molecules are rearranged, all facing the direction perpendicular to the polarization direction of the irradiated light, and are isotropic to the irradiated light, so there is no deflection effect, and the light can pass directly. To realize two-dimensional DIC imaging, an electrical control component can be used to generate high-frequency alternating current. When no voltage is applied to the xLCPG and a voltage is applied to the yLCPG, DIC imaging in the x direction can be realized; similarly, when a voltage is applied to the xLCPG and a voltage is not applied to the yLCPG, DIC imaging in the y direction can be realized. When the frequency of change is high enough, two-dimensional DIC imaging can be realized. In addition, when voltage is applied to both the xLCPG and the yLCPG, bright field imaging can be realized, so that free switching between DIC imaging and bright field imaging can be realized.

[0016] Preferably, the laser is any one of a semiconductor laser and a solid-state laser.

[0017] Preferably, the light aperture of the active LCPG is 10-30 mm, which is larger than the imaging field of view of the microscope objective.

[0018] Preferably, the spacing between the two LCPG groups is less than 20 mm to achieve micrometer-level quantitative differential interference contrast imaging resolution.

[0019] Preferably, the microscope system includes a microscope objective lens and a tube lens, and the working distance of the microscope objective lens is greater than or equal to 30 mm to provide sufficient adjustment space and meet the imaging requirements of larger volume samples.

[0020] Preferably, the resolution of the polarization camera is greater than 1024×1024.

[0021] According to the second aspect of the present specification, a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating and a transmission-reflection integrated type is provided, and the user can freely choose transmission or reflection imaging to observe the sample as needed. The system includes five parts: an illumination system component, an active liquid crystal polarization grating component, a microscopy system component, a mechanical control component, and an electrical control component. The illumination system component includes a liquid crystal phase retarder, and the electrical control component can control the working state of the liquid crystal phase retarder, thereby controlling the polarization state of the irradiated light, and realizing the conversion between transmission and reflection.

[0022] The working process of the reflective type is basically the same as the working process of the system described in the first aspect. The electrical control component controls the working state of the liquid crystal phase retarder so that the illumination light becomes linearly polarized light after passing through, and the optical switch after the liquid crystal phase retarder works in the transmission state. The subsequent working process is the same as the system described in the first aspect.

[0023] The working process of the transmission type is as follows: circularly polarized light is generated by the illumination system components through the liquid crystal phase retarder, and then acts on the sample after being reflected by the optical switch and the reflector; the circularly polarized transmitted light with sample information becomes linearly polarized light after passing through the λ / 4 wave plate, and is divided into two orthogonal circularly polarized light beams with the same sample information with extremely small lateral shear distance under the action of the liquid crystal polarization grating; after passing through the microscope system, the orthogonal circularly polarized light interferes on the photosensitive surface of the polarization camera, forming a differential interference effect; four differential interference contrast images with different phase delays are simultaneously recorded by the polarization camera, and accurate quantitative DIC images are calculated using the phase shift method.

[0024] The advantages of the present invention are:

[0025] 1. Based on the powerful light field control capability of active liquid crystal grating, the present invention can realize two-dimensional quantitative DIC imaging through special optical path design, solving the problem that traditional DIC imaging system can only perform nonlinear imaging in one direction;

[0026] 2. The present invention uses a smaller liquid crystal grating to replace the larger optical refractive element in the traditional DIC system, achieving a more compact optical path design, meeting the current demand for miniaturized and lightweight optical devices, and is easy to integrate into other microscopic imaging equipment to achieve multimodal imaging, greatly expanding its application range;

[0027] 3. The present invention adopts an active liquid crystal grating and controls the state of liquid crystal molecules through an external circuit, which can realize rapid switching of imaging modes between bright field imaging and two-dimensional quantitative DIC imaging, meeting the needs of sample observation under different conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the active liquid crystal polarization grating in the non-powered state according to an embodiment of the present invention.

[0029] Figure 2 FIG. 4 is a schematic diagram of the structure of the active liquid crystal polarization grating in the power-on state according to an embodiment of the present invention.

[0030] Figure 3 Schematic diagram of the structure of the active liquid crystal polarization grating component in an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating provided in Example 1 of the present invention, wherein the solid arrows are light rays and the long dashed lines are electrical connection lines.

[0032] Figure 5 This is a schematic diagram of a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating provided in Example 2 of the present invention, wherein the solid arrows are reflective light path rays, the short dashed arrows are transmissive light path rays, and the long dashed lines are electrical connection lines.

[0033] Figure 6 Schematic diagram of the phase distribution of the sample used in the embodiment of the present invention. The sample is a phase step with a size of 30μm×60μm, a bottom phase of 0, a top phase of π / 2, and uniformly gradient phase slopes with a width of 10μm on both sides.

[0034] Figure 7 This is a diagram showing the effect of two-dimensional quantitative DIC imaging of a sample by the two-dimensional differential interference quantitative phase microscopy imaging system provided in an embodiment of the present invention.

[0035] Figure 8This is a diagram showing the effect of performing phase recovery on two-dimensional quantitative DIC imaging results according to an embodiment of the present invention.

[0036] Fig. 9 for Figure 7 , Figure 8 Phase cross-section comparison diagram at the same position, where the black solid line is the true phase of the sample, and the red dotted line is the result after imaging and phase restoration according to an embodiment of the present invention.

[0037] Figure 3 Part numbers and names: 301-xLCPG, 302-yLCPG, 303-1 / 4 wave plate.

[0038] Figure 4 Parts numbers and names: 401-light source, 402-filter, 403-beam expander lens, 404-collimating lens, 405-linear polarizer, 406-beam splitter, 407-xLCPG, 408-yLCPG, 409-λ / 4 wave plate, 410-sample, 411-microscope objective, 412-tube lens, 413-polarization camera, 414-electrical control assembly.

[0039] Figure 5 Parts numbers and names: 501-light source, 502-filter, 503-beam expander lens, 504-collimating lens, 505-liquid crystal phase retarder, 506-beam splitter, 507-xLCPG, 508-yLCPG, 509-λ / 4 wave plate, 510-sample, 511-microscope objective, 512-tube lens, 513-polarization camera, 514-electrical control assembly, 515-optical switch, 516-reflector. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Embodiment 1:

[0042] See attached Figure 4 This embodiment provides an implementation scheme of a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating, including five parts: an illumination system component, an active liquid crystal polarization grating component, a microscopy system component, a mechanical control component, and an electrical control component.

[0043] In this embodiment, the illumination system assembly is composed of a 532 nm laser light source 401, a 532 nm filter 402, a beam expander lens 403, a collimator lens 404, and a linear polarizer 405, and is used to provide a suitable illumination light source for the sample.

[0044] In this embodiment, the active liquid crystal polarization grating assembly is composed of two active xLCPGs 407, two active yLCPGs 408, and a λ / 4 wave plate 409, wherein the design period Λ of the xLCPG and yLCPG is 12 mm, the aperture is 20 mm, the device thickness is 2 mm, and the spacing d between the two LCPG groups is adjustable in the range of 0.5 mm to 9.5 mm, which is controlled by a mechanical control assembly (not shown in the figure), and can achieve two-dimensional quantitative DIC imaging with a lateral shear distance 2Δ freely adjustable from 400 nm to 1200 nm.

[0045] In this embodiment, the microscopic system component is composed of a microscope objective lens 411, a tube lens 412, and a polarization camera 413 to realize the function of microscopic imaging. Among them, the magnification of the microscope objective lens is 20×, the numerical aperture NA=0.42, the working distance is 30mm, and the tube lens and the microscope objective lens form a microscopic system. The polarization camera is used to simultaneously collect 4 images with different polarization states, and accurate two-dimensional differential interference quantitative phase imaging can be achieved after computer processing.

[0046] In this embodiment, the electrical control component 414 can generate high-frequency alternating current as needed to control the working state of the active liquid crystal polarization grating, thereby achieving two-dimensional differential interference contrast imaging and rapid switching between different imaging modes.

[0047] The working process of this embodiment is described in detail below:

[0048] See attached Figure 4 , a 532nm linearly polarized parallel beam is generated by the illumination system component, and is reflected downward by the beam splitter 406 and passes through the active liquid crystal polarization grating component. The linearly polarized light can be regarded as consisting of left-handed circularly polarized light and right-handed circularly polarized light, so the active liquid crystal polarization grating can split the linearly polarized parallel beam into two left-handed circularly polarized beams and right-handed circularly polarized beams with a certain lateral shear distance 2Δ, where Δ is calculated as follows:

[0049]

[0050] Where λ is the wavelength of the irradiated light, Λ is the design period of the liquid crystal polarization grating, d0 is the thickness of a single liquid crystal polarization grating, and d is the spacing between two LCPG groups (see Appendix Figure 3). The size of Δ determines the accuracy of DIC imaging. For samples with fast phase spatial changes, i.e., high-frequency phase information, a too large Δ value will cause large errors in the gradient measurement of quantitative DIC, thus affecting the imaging quality and the accuracy of phase recovery.

[0051] After passing through the λ / 4 wave plate, two beams of orthogonal circularly polarized light form two beams of orthogonal linearly polarized light that do not interfere with each other, and are respectively irradiated onto two adjacent areas of the sample 410, and the distance between the two areas is 2Δ. The reflected light is merged into a beam after passing through the active liquid crystal polarization grating component. The light field information of the two different areas is superimposed to produce a differential effect, and finally form a differential interference contrast image. After passing through the microscope system, the reflected light is finally imaged on the photosensitive surface of the polarization camera. Due to the special design of the polarization camera, 4 images with different polarization states can be recorded simultaneously, which can be considered as 4 DIC images with phase delays of 0, π / 2, π, and 3π / 2, respectively. Finally, the phase shift method can be used to calculate an accurate quantitative DIC image. The specific calculation method is as follows:

[0052]

[0053] Among them, G is the gradient information of the sample along a certain direction, and I1, I2, I3, and I4 correspond to four light intensity images with phase delays of 0, π / 2, π, and 3π / 2, respectively.

[0054] Finally, the system can obtain the phase gradient information of the sample in two directions (x direction and y direction) and combine it into two-dimensional gradient information. After computer processing, the phase information of the sample can be restored to achieve accurate quantitative phase imaging.

[0055] The following specifically describes the imaging control process of the electrical control component:

[0056] Bright field imaging mode: The electrical control component applies appropriate DC voltage to the four active liquid crystal polarization gratings to make them work in bright field mode. Light passing through LCPG will not be deflected, thus achieving bright field imaging.

[0057] One-dimensional quantitative DIC imaging mode: the electrical control component does not apply voltage to the xLCPG group (or yLCPG group) to make it work in the DIC imaging mode, and applies a suitable DC voltage to the yLCPG group (or xLCPG group) to make it work in the bright field mode, thereby realizing one-dimensional quantitative DIC imaging of the sample in the x direction (or y direction).

[0058] Two-dimensional quantitative DIC imaging mode: The electrical control component applies high-frequency AC voltage to the xLCPG group and the yLCPG group, making them work alternately in DIC imaging mode and bright field imaging mode, respectively realizing DIC imaging in the x direction and y direction in a very short time, thereby realizing two-dimensional quantitative DIC imaging of the sample.

[0059] Embodiment 2:

[0060] In this embodiment, based on the first embodiment, the original optical path is modified to realize a two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating and transmission and reflection. The user can freely choose transmission or reflection imaging to observe the sample according to the needs.

[0061] See attached Figure 5 This embodiment provides an implementation scheme of a two-dimensional differential interference quantitative phase microscopy imaging system based on an active liquid crystal polarization grating and a transmission-reflection integrated system, which includes five parts: an illumination system component, an active liquid crystal polarization grating component, a microscopy system component, a mechanical control component, and an electrical control component.

[0062] In this embodiment, the illumination system assembly is composed of a 532nm laser light source 501, a 532nm filter 502, a beam expander lens 503, a collimator lens 504, and a liquid crystal phase retarder 505, and is used to provide a suitable illumination light source for the sample.

[0063] In this embodiment, the active liquid crystal polarization grating assembly is composed of two active xLCPGs 507, two active yLCPGs 508, and a λ / 4 wave plate 509, wherein the design period Λ of the xLCPG and yLCPG is 12 mm, the aperture is 20 mm, the device thickness is 2 mm, and the spacing d between the two LCPG groups can be adjusted in the range of 0.5 mm to 9.5 mm, which is controlled by a mechanical control assembly (not shown in the figure), and can achieve two-dimensional quantitative DIC imaging with a lateral shear distance 2Δ freely adjustable from 400 nm to 1200 nm.

[0064] In this embodiment, the microscope system component is composed of a microscope objective lens 511, a tube lens 512, and a polarization camera 513 to realize the function of microscopic imaging. Among them, the magnification of the microscope objective lens is 20×, the numerical aperture NA=0.42, the working distance is 30mm, and the tube lens and the microscope objective lens form a microscope system. The polarization camera is used to simultaneously collect 4 images with different polarization states, and accurate two-dimensional differential interference quantitative phase imaging can be achieved after computer processing.

[0065] In this embodiment, the electrical control component 514 can generate high-frequency alternating current as needed to control the working state of the active liquid crystal polarization grating, thereby realizing two-dimensional differential interference contrast imaging and rapid conversion between different imaging modes. At the same time, the electrical control component can control the working state of the liquid crystal phase retarder, thereby controlling the polarization state of the irradiated light and realizing the conversion between transmission and reflection.

[0066] The working process of this embodiment is described in detail below:

[0067] See attached Figure 5 The reflective working process of this embodiment is basically the same as that of the first embodiment. The electrical control component controls the working state of the liquid crystal phase retarder so that the illumination light becomes linearly polarized light after passing through, and the optical switch 515 works in the transmission state. The subsequent working process is the same as that of the first embodiment.

[0068] See attached Figure 5 The working process of the transmission type of this embodiment is as follows: the electrical control component controls the working state of the liquid crystal phase retarder, so that the illumination light becomes circularly polarized light after being transmitted, and the optical switch 515 works in the reflection state. The circularly polarized illumination light acts on the sample 510 after being reflected by the optical switch 515 and the reflector 516. The circularly polarized transmission light with sample information becomes linearly polarized light after passing through the λ / 4 wave plate, and is divided into two orthogonal circularly polarized lights with the same sample information with a very small lateral shear distance 2Δ under the action of the liquid crystal polarization grating. After passing through the microscope system, interference finally occurs on the photosensitive surface of the polarization camera, forming a differential interference effect, and simultaneously recording 4 differential interference contrast images with different phase delays, and finally forming an accurate two-dimensional quantitative DIC image after being processed by a computer.

[0069] The following specifically describes the imaging control process of the electrical control component:

[0070] Reflective imaging mode: The electrical control component controls the liquid crystal phase retarder and the optical switch, so that the liquid crystal phase retarder works in the linear polarization mode and the optical switch works in the transmission mode, thereby realizing reflective imaging.

[0071] Transmission imaging mode: the electrical control component controls the liquid crystal phase retarder and the optical switch, so that the liquid crystal phase retarder works in the circular polarization mode and the optical switch works in the reflection mode, thereby realizing transmission imaging.

[0072] Bright field imaging mode: The electrical control component applies appropriate DC voltage to the four active liquid crystal polarization gratings to make them work in bright field mode. Light passing through LCPG will not be deflected, thus achieving bright field imaging.

[0073] One-dimensional quantitative DIC imaging mode: the electrical control component does not apply voltage to the xLCPG group (or yLCPG group) to make it work in the DIC imaging mode, and applies a suitable DC voltage to the yLCPG group (or xLCPG group) to make it work in the bright field mode, thereby realizing one-dimensional quantitative DIC imaging of the sample in the x direction (or y direction).

[0074] Two-dimensional quantitative DIC imaging mode: The electrical control component applies high-frequency AC voltage to the xLCPG group and the yLCPG group, making them work alternately in DIC imaging mode and bright field imaging mode, respectively realizing DIC imaging in the x direction and y direction in a very short time, thereby realizing two-dimensional quantitative DIC imaging of the sample.

[0075] Figure 6 Schematic diagram of the phase distribution of the sample used in the embodiment of the present invention. The sample is a phase step with a size of 30μm×60μm, a bottom phase of 0, a top phase of π / 2, and uniformly gradient phase slopes with a width of 10μm on both sides.

[0076] Figure 7 This is a diagram showing the effect of two-dimensional quantitative DIC imaging of a sample by the two-dimensional differential interference quantitative phase microscopy imaging system provided in an embodiment of the present invention. Figure 8 This is a diagram showing the effect of performing phase recovery on two-dimensional quantitative DIC imaging results according to an embodiment of the present invention.

[0077] Fig. 9 for Figure 7 , Figure 8 Phase cross-section comparison diagram at the same position, where the black solid line is the true phase of the sample, and the red dotted line is the result after imaging and phase restoration according to an embodiment of the present invention.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating, characterized in that: It includes an illumination system component, an active liquid crystal polarization grating component, a microscope system component, a mechanical control component, and an electrical control component; The lighting system component is used to provide a lighting source for the sample; The active liquid crystal polarization grating assembly is arranged behind the sample, and includes two LCPG groups, each group includes one active LCPG with periodic change direction of liquid crystal molecules in the x direction, and one active LCPG with periodic change direction of liquid crystal molecules in the y direction, and the spacing between the two LCPG groups is adjusted by the mechanical control assembly; The microscopic system component includes a microscopic system and a polarization camera; the microscopic system is arranged behind the active liquid crystal polarization grating component to realize microscopic imaging; the polarization camera is arranged behind the microscopic system to realize differential interference quantitative phase microscopic imaging; The electrical control component is connected to four pieces of LCPG and is used to control the arrangement state of the LCPG liquid crystal molecules, thereby realizing multi-directional DIC imaging and switching between different imaging modes.

2. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 1, characterized in that: The electrical control component applies a DC voltage to the four LCPG sheets so that they work in a bright field imaging mode; The electrical control component does not apply voltage to xLCPG, so that it works in DIC imaging mode, and applies DC voltage to yLCPG, so that it works in bright field imaging mode, thereby realizing one-dimensional quantitative DIC imaging of the sample in the x direction; The electrical control component does not apply voltage to yLCPG, so that it works in DIC imaging mode, and applies DC voltage to xLCPG, so that it works in bright field imaging mode, thereby realizing one-dimensional quantitative DIC imaging of the sample in the y direction; The electrical control component applies high-frequency AC voltage to xLCPG and yLCPG, so that they work alternately in DIC imaging mode and bright field imaging mode, respectively realizing DIC imaging in the x direction and y direction in a very short time, thereby realizing two-dimensional quantitative DIC imaging of the sample.

3. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 1, characterized in that: The microscope system includes a microscope objective lens and a tube lens, and the working distance of the microscope objective lens is greater than or equal to 30 mm; the light aperture of the active LCPG is 10-30 mm, which is larger than the imaging field of view of the microscope objective lens.

4. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 1, characterized in that: The mechanical control component is used to adjust the distance between the two LCPG groups, so as to adjust the resolution; the distance between the two LCPG groups is less than 20 mm, so as to achieve micron-level quantitative differential interference contrast imaging resolution.

5. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 1, characterized in that: The system forms reflective imaging through a linear polarization polarizer, specifically: A linearly polarized parallel light beam is generated by the illumination system component through a linear polarization polarizer, and is reflected downward by a beam splitter to pass through an active liquid crystal polarization grating component; the active liquid crystal polarization grating divides the linearly polarized parallel light beam into two left-handed circularly polarized light beams and right-handed circularly polarized light beams with a transverse shear distance; After passing through the λ / 4 wave plate, two beams of orthogonal circularly polarized light are formed into two beams of orthogonal linearly polarized light that do not interfere with each other, and are respectively irradiated onto two adjacent areas of the sample; the reflected light is merged into one beam after passing through the active liquid crystal polarization grating component, and the light field information of the two different areas is superimposed to produce a differential effect, forming a differential interference contrast image; After passing through the microscope system, the reflected light is imaged on the photosensitive surface of the polarization camera; four images with different polarization states are recorded simultaneously by the polarization camera, and accurate quantitative DIC images are calculated using the phase shift method.

6. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 5, characterized in that: The calculation formula of the transverse shear distance 2Δ is as follows: Where λ is the wavelength of the irradiated light, Λ is the designed period of the liquid crystal polarization grating, d0 is the thickness of a single liquid crystal polarization grating, and d is the spacing between two LCPG groups.

7. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 5, characterized in that: The calculation formula of the quantitative DIC image is: Where G is the gradient information of the sample along a certain direction, and I1, I2, I3, and I4 correspond to four light intensity images with phase delays of 0, π / 2, π, and 3π / 2, respectively.

8. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 1, characterized in that: The system is a transmissive-reflective integrated system formed by a liquid crystal phase retarder and an optical switch. The electrical control component controls the working state of the liquid crystal phase retarder, thereby controlling the polarization state of the irradiated light to achieve the conversion between the transmissive and reflective modes. Specifically: The electrical control component controls the liquid crystal phase retarder and the optical switch, so that the liquid crystal phase retarder works in a linear polarization mode and the optical switch works in a transmission mode, thereby realizing a reflective imaging mode; The electrical control component controls the liquid crystal phase retarder and the optical switch, so that the liquid crystal phase retarder works in a circular polarization mode and the optical switch works in a reflection mode, thereby realizing a transmission imaging mode.

9. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 8, characterized in that: The reflective imaging mode is specifically: The linear polarized light is generated by the illumination system component through the liquid crystal phase retarder, and after being transmitted through the optical switch, it is reflected by the beam splitter and passes downward through the active liquid crystal polarization grating component; the active liquid crystal polarization grating divides the linear polarized light into two left-handed circularly polarized light beams and right-handed circularly polarized light beams with a lateral shear distance; After passing through the λ / 4 wave plate, two beams of orthogonal circularly polarized light are formed into two beams of orthogonal linearly polarized light that do not interfere with each other, and are respectively irradiated onto two adjacent areas of the sample; the reflected light is merged into one beam after passing through the active liquid crystal polarization grating component, and the light field information of the two different areas is superimposed to produce a differential effect, forming a differential interference contrast image; After passing through the microscope system, the reflected light is imaged on the photosensitive surface of the polarization camera; four images with different polarization states are recorded simultaneously by the polarization camera, and accurate quantitative DIC images are calculated using the phase shift method.

10. The two-dimensional differential interference quantitative phase microscopy imaging system based on active liquid crystal polarization grating according to claim 8, characterized in that: The transmission imaging mode is specifically: The illumination system generates circularly polarized light through a liquid crystal phase retarder, which reacts with the sample after being reflected by an optical switch and a reflector. The circularly polarized transmitted light with sample information becomes linearly polarized light after passing through the λ / 4 wave plate, and is divided into two orthogonal circularly polarized lights with the same sample information with a very small lateral shear distance under the action of the liquid crystal polarization grating; After passing through the microscope system, the orthogonal circularly polarized light interferes on the photosensitive surface of the polarization camera, forming a differential interference effect; the polarization camera simultaneously records four differential interference contrast images with different phase delays, and the phase shift method is used to calculate an accurate quantitative DIC image.

Images